Outcrossing rates and levels of correlated outcrossing within and between fruits were estimated for Venezuelan cacti with contrasting mating and pollination systems: (a) Two columnar cacti, Stenocereus griseus and Cereus repandus, both self-incompatible and predominantly bat-pollinated; and (b) one globose cactus, Melocactus curvispinus, self-compatible and predominantly hummingbird-pollinated. Estimations were conducted on a single population of each species in Central Venezuela using five allozyme loci. S. griseus and C. repandus were predominantly outcrossing at the population (tm = 0.926 1.00) and individual (mean tm = 0.930 0.960) levels and had negligible levels of biparental inbreeding (<2%). M. curvispinus behaved as a facultatively xenogamous species with significant selfing at both population (tm = 0.764) and individual (mean tm = 0.18 1.00) levels. No biparental inbreeding was detected for the population studied. Overall, outcrossing rates for the three cacti were consistent with their mating systems. Our results indicate that bats and hummingbirds promote outcrossing on these plants; however, animal-mediated outcrossing of Melocactus flowers is not guaranteed. The two columnar cacti had relatively low correlations of outcrossed progeny among fruits within a maternal plant (rp = 0.050 0.158), but correlated paternity increased significantly within fruits, with substantial differences between S. griseus (rp = 0.852) and C. repandus (rp = 0.228). For M. curvispinus, correlated paternity among fruits within a family was low (rp = 0.059) and increased moderately within fruits (rp = 0.198). These results suggest that, for the three cacti, outcrossed progeny was primarily the product of multiple pollen donors. This pattern is consistent with the foraging strategies of the pollinators associated with these plants; however, at the flower level, correlated paternity can become an important factor increasing genetic relatedness within families.

Key words: cactus, Cereus repandus, correlated matings, mating system, Melocactus curvispinus, Stenocereus griseus